JP2000357988A - Method and apparatus for synchronization among base stations - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a function for synchronizing a system clock with a UTC (coordinated universal time) time C at GPS unlock time. SOLUTION: When the UTC time is obtained due to a state, where a GPS (position measuring system) receiver cannot catch a GPS satellite or is not locked to the UTC time collected from the GPS satellite though the satellite is caught (the state is called GPS unlock in the following.) concerning the synchronizing function using the receiver in a method for synchronization among base stations for obtaining synchronization in a clock among a plurality of base stations, the reception destination of the UTC time is changed-over into the interface of a transmission line for connecting the base stations, a UTC time C of another base station is received, a delay correcting value in the case of locking to the UTC time is added to the UTC time C, and a synchronization state among the base stations is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-base-station synchronization method and an inter-base-station synchronization apparatus in which a plurality of base stations synchronize with each other or in accordance with UTC time (international standard time) by GPS reception.

[0002]

2. Description of the Related Art In a system that uses a GPS receiver to synchronize the system clocks between base stations, the system between the base stations when the GPS receiver is unlocked from the GPS clock for satellite communication and enters the GPS unlocked state. Synchronization is performed using a crystal oscillator with a thermostat (TC
The method of self-propelled operation that relies on the accuracy of XO) was used.

Here, as a conventional example 1, Japanese Patent Laid-Open No.
No. 7932 discloses a GP that is used for phase correction between transmission signals from a mobile communication base station and in which a plurality of base stations are set.
The present invention relates to a TDM synchronization method between mobile communication base stations that can simultaneously transmit synchronously based on the S time, so that one of the other neighboring base stations establishes synchronization with the reference neighboring base station. A sequential transmission synchronization method in which the time is corrected and the delay time is sequentially corrected one-to-one such that one of the other peripheral base stations establishes synchronization based on the corrected peripheral base station. To solve the problem that complicated steps and long time are required until synchronization is finally established, and the delay correction completion time increases in proportion to the number of neighboring base stations. It is an object.

[0004] In the same publication, therefore, each peripheral base station,
Receiving a call signal and a GPS time from a GPS satellite using satellite communication, generating a GPS clock based on the GPS time, detecting a delay time of the call signal based on the generated GPS clock, It is described that the phase delay of the ringing signal is corrected based on the count number of the time obtained by subtracting the delay time from the cycle time of the GPS clock, and the ringing signal is transmitted to the receiver after the correction. Even if various delay times occur when a call signal is transmitted from the central base station to each peripheral base station, each peripheral base station is synchronized with the cycle of the GPS clock generated based on the GPS time received from the GPS satellite. It is described that since the stations can simultaneously transmit a paging signal, synchronization of the paging signal is instantaneously established.

[0005]

SUMMARY OF THE INVENTION However, GPS
Even if synchronization of the calling signal is instantaneously established in synchronization with the clock cycle, in the case of the GPS unclocked state, it depends on the free-running clock of the crystal oscillator with the thermostat, so the phase of the oscillating clock is However, the phase shift occurred for some reason and could not be corrected.

Therefore, the present invention provides a GPS receiver
When the unlocked state is reached, another B is set for free-running operation by the crystal oscillator with a constant temperature layer in the clock supply card.
Based on UTC (Coordinated Universal Time) time B received from a TS (Base Terminal Station),
An object of the present invention is to provide a function of synchronizing a system clock with a UTC time by using a UTC time C in which a correction calculation is performed in consideration of a delay due to a traffic situation with another BTS.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for synchronizing clocks between a plurality of base stations.
When a GPS (position measurement system) receiver provided in each of the base stations cannot acquire a GPS satellite and is not locked at UTC time A (international standard time) (hereinafter, referred to as GPS unlocked), The receiving destination of UTC time A is switched to the interface of the transmission path connecting the base stations, and the UTC time B of the other base station is received, and the UTC time B is received.
A synchronous state between the base stations is maintained as a UTC time C by adding a delay correction value when the GPS lock is performed at the UTC time A to the TC time B.

Further, the present invention relates to an inter-base station synchronizer for synchronizing clocks between a plurality of base stations, wherein the base station obtains UTC time A (international standard time) from a GPS (position measurement system) satellite. A GPS receiver for receiving,
A clock generator for generating a clock signal synchronized with the TC time A, and a calculation for calculating a delay correction value according to a delay time between the UTC time A and the UTC time B input from another base station via a transmission line Unit, and a memory unit for storing the traffic state of the transmission path and the delay correction value,
When the UTC time A cannot be captured from the GPS receiver, a synchronized clock signal is generated by adding the delay correction value to the UTC time B.

[0009] The inter-base station synchronization function according to the present invention includes:
Regarding the synchronization function using the GPS receiver, the UTC is used in order to prevent the GPS receiver from acquiring the satellite or to acquire the satellite but lock the satellite at the time of acquisition from the satellite (hereinafter, referred to as GPS unlock). When the time (international standard time) cannot be obtained, the function of automatically switching the reception destination of the UTC time to the transmission line I / F and receiving the UTC time of another BTS to maintain the synchronization state between base stations It is characterized by.

The present invention also relates to a system including the inter-base-station synchronization function shown in FIG.
BTS2 and BTS3 are UTs obtained from GPS receivers.
By generating a system clock synchronized with the C time, synchronization between base stations is achieved. At this time, the BTS1 and the BTS2 always transmit the UTC time received by each GPS receiver via the exchange MCC at a constant cycle through the transmission lines 1 and 2.
To send and receive. When receiving the UTC time from the transmission line, the UTC time is compared with the UTC time from the own GPS receiver, and the result of calculating the transmission line delay is stored in the memory as a correction value.
By periodically receiving the UTC time from the transmission path, it is possible to obtain a calculated value for each traffic state on the transmission path. Therefore, it is possible to obtain an optimal correction value by obtaining the traffic state between BTS2 and BTS1.

When the GPS receiver of the BTS 1 is in the GPS unlocked state and the UTC time cannot be obtained from the GPS receiver of the own device, the BTS 1
The C time input is switched from the GPS receiver to the transmission path I / F.

After switching to the transmission line I / F side, the system clock is generated in a free-running state of the crystal oscillator with a constant temperature layer in the apparatus. When the UTC time is received from the BTS2, the BTS2 ~ BTS1
Correction is performed at UTC time B, where correction is performed in consideration of transmission path delay between the base stations, and phase synchronization is performed with respect to UTC time, thereby maintaining synchronization between base stations.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described.
This will be described in detail with reference to the drawings.

(1) Description of Configuration FIG. 1 shows a system diagram for the inter-base station synchronization function according to the present embodiment. In the figure, base station apparatuses BTS1, BTS
2. The BTS 3 generates a UTC time as a GPS (Global Positioning System) system using three or more satellites for satellite communication, and mainly generates a UTC time in addition to searching a ground position. In this case, a system clock synchronized with UTC time A obtained from the GPS receiver is used to synchronize between base stations. At this time, the BTS1 and the BTS2 transmit and receive the UTC time A received by the respective GPS receivers via the transmission lines 1 to 3 via the exchange MCC at a constant cycle. UTC
When the time B is received from the transmission lines 1 to 3, the GPS
The result of comparing with the UTC time A from the receiver and calculating the transmission path delay is stored in a memory as a correction value. UTC
By receiving the time B periodically from the transmission paths 1 to 3, it is possible to obtain a calculated value for each traffic state on the transmission paths 1 to 3. Therefore, by obtaining the traffic state between BTS2 and BTS1, the optimum value is obtained. A delay time correction value can be obtained.

Referring to FIG. 2, there is shown a clock system of a base station apparatus including an inter-unit synchronization function according to the present embodiment.

The inter-station synchronization function receives a GPS receiver 1 demodulated from a GPS antenna input, and a HWY unit 2 that receives UTC time B of another base station and sends UTC time A to another base station. And a difference between UTC time B and a calculation unit 3, a memory 4 for storing a correction value of UTC time B in advance, and a clock generation unit 5 for generating a reference clock in the base station.

Here, the GPS receiver 1 captures a GPS satellite and locks at a time collected from the GPS satellite (hereinafter referred to as G
The UTC time obtained by performing the PS lock is input to the clock generator 5, the arithmetic unit 3, and the HWY unit 2.

The clock generator 5 can obtain the UTC time A from the GPS receiver 1 and the UTC time C from the arithmetic unit 3 and select either one according to the GPS lock state of the GPS receiver 1. As a result, a system clock synchronized with the UTC time is always generated. That is, in the GPS locked state, the UTC time from the GPS receiver 1 is selected, and in the GPS unlocked state, the UTC time C from the arithmetic unit 3 is selected, so that the time inside the clock generation unit 5 is set. Corrects the counter and generates a clock synchronized with the time counter.

At this time, the UTC time A or the UTC time C is selected by the GPS unlock AL from the GPS receiver 1.
Switching is performed by the M signal.

The HWY unit 2 exchanges ATM cells of an ATM (asynchronous mode) system with the exchange MCC as an interface I / F of a transmission line.

The HWY unit 2 is connected to the exchange MCC via a transmission line.
Is the UTC time from the GPS receiver 1, and the data received from the MCC is the UTC time from another BTS, and transmits the UTC time to the arithmetic unit 3.

The operation unit 3 receives the UTC received from the HWY unit 2
Time B and UTC time A input from GPS receiver 1
And calculates a transmission path delay from another BTS at UTC time B, and stores it in the memory unit 4.

At this time, the traffic state of the transmission line is also stored in the memory unit 4. This is because, when transmitting the UTC time C to the clock generator 5, the correction value stored in the memory unit 4 is statistically calculated using the correction value of the approximate traffic condition, and is received from another BTS. This is because the UTC time is corrected to UTC time C.

(2) Description of Operation Hereinafter, the operation of this embodiment will be described with reference to the configuration of FIG. 2 and the sequence diagram of FIG.

As an example, between two devices (BTS1, BTS1)
The operation at 2) will be described. When the GPS receiver 1 is in the GPS locked state, the UTC
The exchange of the time A and B information is performed in the transmission path 1 and the transmission path 2 via the MCC at a fixed cycle (S1, S2, S
21, S22).

At this time, a dedicated VCI (virtual channel identifier) and VPI (virtual path identifier) connection by the ATM system is set between the BTS1 and the MCC and the BTS2, so that the connection through the transmission lines 1 and 2 is prevented. Cell delay and the like due to the communication of the cell.

The clock generator 5 oscillates a system clock in synchronization with UTC time A from the GPS receiver 1 (S3, S23). This system clock is synchronized with UPC time A by a PLL circuit or the like using a crystal oscillator with a temperature compensation circuit as an original oscillation circuit.

The arithmetic unit 3 calculates a correction value from the UTC time B input from the HWY 2 and the UTC time A from the GPS receiver 1 (S4, S24), and calculates the correction value and the transmission line at that time. Is stored in the memory 4 together with the traffic situation (S5, S25).

While both the BTS 1 and the BTS 2 maintain the GPS locked state, the arithmetic unit keeps storing the correction value calculation result and the traffic status of the transmission line in the memory 4. This correction value is updated periodically. In addition, exchange M by satellite communication
If the environment state of the CC changes and the delay characteristic of the transmission path changes with a high probability, the periodic time is shortened and the correction value is updated.

Also, BTS1 and BTS2 are both GPS
While the lock state is maintained, the clock generator 5
It is used only to obtain a correction value calculation result for the UTC time B input from the WY unit 2. At this time, UTC time A and UTC time C corrected by the correction value based on UTC time B are synchronously coincident with each other, and even when pulse generator 5 is synchronized with UTC time A, The input of the pulse generator 5 has a transmission line delay corrected UT
C Time C is supplied.

Here, when the BTS1 is in the GPS unlocked state, an alarm is generated (S6), and the UTC time A is transmitted and received from the BTS2 (S26, S).
7). The clock generation unit 5 of the BTS 1 converts the input of the UTC time B into G according to the GPS unlock signal from the GPS receiver 1.
Switching from the PS receiver 1 to the calculation unit 3 (S8), calculating a correction value of the phase shift (synchronization shift) (S9), storing the correction value in the memory 4, and performing the input / output from the transmission path data input / output transmitted from the BTS 2 Oscillates and outputs a system clock synchronized with UTC time C (S10). Thereafter, the clock generator 5 continues the oscillation synchronized with the UTC time C (S1).
1). This state continues until the GPS receiver 1 enters the GPS locked state.

Using the timing chart of FIG.
The operation of the clock generator 5 at time C will be described. FIG.
Shows state diagrams of a GPS locked state and a GPS unlocked state.

The system clocks f1 and f2 are synchronized with the UTC time A. Here, the system clock f1 is a clock obtained by dividing the system clock f2, and is appropriately used in the system. At this time, U
It is assumed that TC time C is corrected with respect to UTC time A by a correction value n4 seconds.

During reception of UTC time A, the GPS is locked, and the internal time counter counts in synchronization with UTC time A. On the other hand, when the GPS unlock state is reached, the operation is synchronized with UTC time C, and the clock generation unit 5 generates the UTC time C obtained by adding the correction value to UTC time B.
Generates a clock in synchronization with

At this time, the synchronous operation of the internal counter at the UTC time C is determined according to the correction value at the time of t1 + n4 seconds.
The operation is the same as when the internal time counter is synchronized with time A. Thus, the clock phase can be maintained.
In FIG. 4, the count value of the internal counter is the time t.
1, t2, t3, and correction values n1, n2,. It shows a state where n5 is corrected and updated.

A calculation example of the calculation unit 3 will be described with reference to the sequence diagram of FIG.

First, the operation of the arithmetic unit 3 when no GPS ALM has occurred, that is, in the normal state, will be described. BTS2
Sets UTC time A from its own GPS receiver 1 to exchange M
When transmitting to the BTS 1 via CC, the transmission is performed in the ATM cell format for time information transmission shown in FIG. In FIG. 5 (b), a 5-byte area is allocated for the ATM header, and then a part, b part, and c part
The UTC time a of TS2, the reception time b when received by the MCC switch, and the transmission time c when transmitted by the MCC switch are inserted. Further, a fixed pattern is assigned after the time c. The data is transmitted from the exchange MCC to the BTS 1 in the format shown in FIG. 5B and received by the BTS 1.

The BTS 1 obtains times a, b, and c, and the arithmetic unit 3 obtains the following values.

Transmission delay between BTS2 and exchange MCC T1 = ba Internal delay of exchange MCC T2 = cb Transmission delay between MCC and BTS1 T3 = UTC time obtained by BTS1 from GPS receiver-c Transmission delay between BTS2 and BTS1 T4 = UTC time obtained by BTS1 from the GPS receiver−a Here, T4 is a correction value of the UTC time.

T1, T2, T obtained by the operation unit 3
3 and T4 are stored in the memory unit 4 as one combination.

Next, the operation of the arithmetic unit 3 when the GPS ALM is in the unlocked state when the GPS ALM occurs will be described.

As in the case where no GPS ALM has occurred, BTS1 is the UT of BTS2 in the ATM cell format shown in FIG.
After obtaining the C time, the reception time when the MCC exchange receives, and the transmission time when the exchange MCC transmits, T1, T
2, but T4 cannot be calculated because GPS ALM is occurring.

Therefore, the operation unit 3 obtains the obtained T1, T2
A combination of the same delay or a similar delay is selected from the contents of the memory unit 4 and is associated (the T1,
T4 (stored together when T2 was stored)
This is used as a UTC correction value. At this time, the obtained T4
Is a value including an error of the transmission delay T3 between the exchanges MCC and BTS1. Therefore, the UTC time C corrected by the correction value
Can be obtained as follows.

UTC time C = UTC time a + T4 of BTS2 According to UTC time C corrected by this correction value,
The clock generator 5 generates a clock signal synchronized with the UTC time C, and supplies the clock signal to units, control panels, and the like of each unit in the BTS 1.

[0045]

According to the present invention, the UTC from other BTSs
UTC that periodically receives time A and corrects the transmission path delay
Since the phase of the free-running clock is corrected at time C, GP
When the S receiver is in the satellite non-capturing state (GPS unlocked state), higher accuracy can be maintained as compared with a conventional system that relies on the accuracy of a crystal oscillator.

[Brief description of the drawings]

FIG. 1 is a system diagram for a synchronization function between base stations according to the present invention.

FIG. 2 is a block diagram illustrating a synchronization function between base stations according to the present invention.

FIG. 3 is a time flowchart showing an inter-base-station synchronization function of the present invention.

FIG. 4 is a timing chart showing the inter-base-station synchronization function of the present invention.

FIG. 5 is a sequence diagram illustrating a synchronization function between base stations and a switch according to the present invention.

[Explanation of symbols]

 1 GPS receiver 2 HWY section 3 Operation section 4 Memory 5 Clock generator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04Q 7/30

Claims (6)

[Claims] 1. An inter-base station synchronization method for synchronizing clocks between a plurality of base stations, comprising:
When the S (position measurement system) receiver is unable to acquire a GPS satellite and is not locked at UTC time A (international standard time) (hereinafter referred to as GPS unlocked), the receiver of the UTC time A Is switched to the interface of the transmission path connecting the base stations, and the U
Receiving a TC time B, adding a delay correction value when the GPS lock is performed at the UTC time A to the UTC time B, and maintaining the synchronization state between the base stations as a UTC time C. Synchronization method between base stations. 2. The inter-base-station synchronization method according to claim 1, wherein the delay correction value is transmitted to the other of the base stations via the transmission path when the delay correction value is locked at the UTC time A (International Standard Time). The UTC time B and the U
A method for synchronizing between base stations, characterized in that the calculation is output based on a difference from TC time A. 3. The inter-base station synchronization method according to claim 1, wherein the transmission path between the base stations is transmitted to another base station by a virtual channel identifier and a virtual path identifier by an ATM system. Base station synchronization method. 4. An inter-base station synchronizer for synchronizing clocks between a plurality of base stations, wherein the base station receives a UTC time A (international standard time) from a GPS (position measurement system) satellite. A clock generator for generating a clock signal synchronized with the UTC time;
TC time A and U input from another base station via a transmission path
A calculating unit for calculating a delay correction value in accordance with a delay time from the TC time B; and a memory unit for storing the traffic state of the transmission line and the delay correction value. When A cannot be captured, the UT
C. An inter-base-station synchronizer, which generates a synchronized clock signal by adding the delay correction value to time B. 5. The inter-base station synchronizer according to claim 4, wherein the delay correction value is transmitted to the other of the other base stations via the transmission path when the base station is locked at the UTC time A (International Standard Time). The UTC time B and the U
An inter-base-station synchronizer, which is calculated and output based on a difference from TC time A. 6. The inter-base-station synchronizer according to claim 4, wherein a transmission path between the base stations is transmitted to another base station by a virtual channel identifier and a virtual path identifier by an ATM system. Synchronizer between base stations.